Electric control system



Dec. 23, 1941. G. w. GARMAN v 2,267,404

ELECTRIC CONTROL SYSTEM Original Filed Nov. 24, 1957 3 Sheets-Sheet l 5 Fig.1.

Inventor: George W Garman,

9 H i s Attorneg.

Dec. 23, 1941. w GARMAN 2,267,404

ELEGTRI C CONTROL SYSTEM Original Filed Nov. 24, 1937 3 Sheets-Sheet 2 fi/S Hi Attorn 8y.

Dec 23, 1941. G, W, ARMAN 2,267,404

ELECTRIC CONTROL SYSTEM Original Filed Nov. 24, 1937 3 Sheets-Sheet 3 Fig. 7.

TOHOTORBQ Fig.6. as 7 76 85 (W184 I 77 83 TRANSFORMER SATURABLF. IYOPRIHL novnz VALVE MECHANISH.

PRIME movER. 82

TRANSFORMER Ge orge W. Garm an,

His Attorney.

Patented Dec. 23, 1941 ELECTRIC CONTROL SYSTEM George W. Garman, Sche to General Electric Co New York nectady, N. Y., assignor mpany, a corporation of Original application November 24, 1937, Serial No.

1940, Serial No. 338,007

4 Claims.

is frequently desirable to control an operation by means of an electric motor the speed of which is precisely and accurately determinable. For example, in many applications it is desirable to energize a direct current motor from an associated alternating current circuit through electric valve means and to maintain the speed of the motor at a definite predetermined speed.

Heretofore many of the prior art arrangements which have been employed for this purpose have entailed the use of complicated and expensive control equipmentand have been susceptible to objectionable variations in speed. Furthermore, it has become desirable to provide control apparatus which is entirely electrical in nature and operation and which is free of moving or vibrating contacts. In addition, it is important in order to obtain precise control to dispense with the use of mechanical speed responsive devices because of the inherent limitations of such arrangements.

It is an object of my invention to provide a new and improved electric control system.

It is another'object of my invention to provide a new and improved electric valve control system for dynamo-electric machines.

It is a further object of my invention to provide a new and improved control system for electric valve translating apparatus for controlling the speed of a direct current motor.

Briefly stated, on one of the illustrated embodiments of my invention I provide a control system for dynamo-electric machines, such as direct current motors, in which a bridge circuit is connectedbetween a pilot generator and control electric valves which determine an operating condition, such as the speed of the motor to be controlled. Suitable anti-hunting or damping circuits are connected between the bridge circuit and the electric valves or electronic discharge devices which control the energization of the motor. The direct current pilot generator which is responsive to a predetermined controlling influence such as the speed of the motor, is connected to the bridge circuit,

and the bridge circuit accentuates the voltage.

Divided and this application May 31,

variations-of the pilot generator to obtain precise and accurate control 01' the motor speed.

In another modification of this aspect of my invention, a dynamo-electric machine of the direct current type, such as a. direct current motor, is provided with a field winding and a pair of armature circuits so that the motor may be rotated in either direction. A pair of rectifying circuits are associated with the respective armature circuits and the conductivity of these rectifying circuits is controlled in response to a predetermined controlling influence, such as the speed of the motor. A pair of electronic discharge devices is provided to control the conductivity of the electric valves in the rectifying circuits. A bridge circuit including nonlinear elements is connected to be responsive to the output voltage of a direct current pilot generator, and anti-hunting or damping circuits are connected between the output circuit of the bridge and the input or grid circuits of the electronic discharge devices.

For a better understanding of my invention, reference may be had to the following description taken inconnection with the accompanying drawings, and its scope will be pointed out in the appended claims. Fig. 1 diagrammatically illustrates an embodiment of my invention as applied to a control system'for a dynamo-electric machine of the direct current type and in R which a pilot generator is connected directly secondary winding ID in circuit with the control members of the power electric valves; Fig. 2 illustrates an embodiment of my invention employing an intermediate control electric valve between the pilot generator and the main or power electric valves; and Figs. 3-6 represent certain modifications thereof. Fig. 7 diagrammatically illustrates another embodiment of my invention as applied to a control system for a direct current motor arranged for operation in both directions of rotation.

Referring now to Fig. 1 of the drawings, my

invention is diagrammatically illustrated as ap-' plied to an electric valve control system for a dynamo-electric machine I of the direct current type having an armature 2 and a field winding 3. The field winding 3 may be energized from any suitable source of direct current 4. Armature 2 of machine I is energized from an alternating current circuit 5 through a transformer 6 and through electric valves 1 and 8. The transformer 6 comprises a primary winding 9 and a provided with electrically intermediate connections H, i2 and I3.

The electric valves 1 and 8 are preferably of the type employing an ionizable medium such as a gas or a vapor and each comprises an anode I4, a cathode I5 and a control means or member I6. One terminal of the direct current armature 2 of machine I is connected to the intermediate connection II of secondary winding I0, and the other terminal thereof is connected to the common connection of cathodes I5 of electric valves 1 and 8.

To impress oncontrol members I6 of electric valves I and 8 alternating voltages of predetermined phase displaced relative to the respective anode voltages, I employ an excitation circuit ineluding a transformer I1 energized from secondary winding III of transformer 6 through a suitable phase shifting circuit I8. The transformer I1 is provided with a primary winding I9 and a secondary winding 20. The phase shifting circuit I8 may comprise a capacitance 2I and a variable resistance 22 having terminals connected to intermediate connections I2 and I3, respectively, of secondary winding III of transformer 6. Primary winding I9 of transformer I1 i connected to the common juncture of capacitance 2| and 24 may be of the direct current type having an armature member 25 and a field winding 26 which may be energized from any suitable source of direct current, and which is shown as being connected to the direct current circuit 4. I provide a voltage divider 21, comprising a resistance 28 and an adjustable contact 29, for producing a variable or adjustable source of reference potential against which the output voltage of the pilot generator 24 acts. The voltage divider 21 may be energized from any suitable source of unidirectional voltage 30. It will be noted that the voltage of the voltage divider 21 and the voltage of the pilot generator 24 act in opposition to introduce in the excitation circuit for electric valves I and 8 a resultant unidirectional voltage which varies in accordance with the speed of the dynamo-electric machine I.

In order to control the rate of change of the system, including the anti-hunting circuit .and the direct current pilot generator, are disclosed and claimed in my above-identified application which is assigned to the assignee of this application. I

The operation of the embodiment of my invention shown in Fig. 1 will be explained by considering the system when dynamo-electric machine I is operating as a direct current motor. A unidirectional current will be transmitted to the armature 2 of machine I through electric valves I and B which operate as a rectifier energized from the alternating current circuit 5.

The manner in which the electric valves I and 8 control the voltage impressed on armature 2 of machine I -will be well understood by those skilled in the art. For a given positive anode voltage there is a certain value of grid voltage which is termed the critical grid voltage. When the grid is more negative than this value, current cannot flow between anode and cathode. If the grid is more positive than this critical value, current can flow and the magnitude of the current will be determined principally by the external resistance of the associated circuit. Once this current is established between anode and cathode, in the usual commercial arrangement thegrid can exert no further control unlessthe anode 'voltage is reduced to a value near zero. When the anode voltage becomes zero, the cure rent flow ceases and if the grid is sufficiently negative it can then prevent the current from restarting. Therefore, when a voltage is applied difierence voltage provided by pilot generator 24 and voltage divider-21 and hence to control the rate of change of potential of control members I6, I provide a serially connected capacitance 3| and a resistance 32 which are connected in series 7 relation with the voltage divider 21 and armature 25 of pilot generator 24. Capacitance 3| and resistance 32 serve as-a damping means for nected in parallel relation with resistance 32.

This-capacitance permits-a rapid rate of change of the potential of control members I6 for small changes in speed of the dynamo-electric machine I. 7

Certain aspects of the electric valve control between the cathode and anode, the grid can regain control once during each cycle and can, therefore, be used to prevent current flow when the anode is positive.

Resistance 22 may be adjusted so that the phase of the alternating components of voltage impressed on control members I6 by transformer I'I lag the respective anode voltages-by substantially degrees. Voltage divider 21 is adjusted so that the voltage which this element introduced into the excitation circuit is somewhat greater than the negative unidirectional biasing potential provided by pilot generator 24. By the proper adjustment of the voltage divider, the resultant unidirectional voltage impressed on the control members I6 will be positive.

If it be assumed that the speed of the dynamoelectric machine I decreases to a value belowthe predetermined range to be maintained, the volt- ,age produced by the pilot generator 24 will correspondingly decrease to efiect an increase in the positive resultant unidirectional voltage impressed on control members I6 of electric valves .1 and 8, thereby effecting a virtual advancement in phase of the resultant voltages impressed on control members I6 and thereby increasing the output voltage of the electric valves 1 and 8 impressed on armature 2 of machine I. By virtue of this increase in voltage," the speed of the machine I will be increased tending to restore it to the predetermined range of operation. On the other hand, if the speed of the machine I increases to a value above the predetermined range of operation, the output voltage, of pilot generator 2I will increase efiecting a decrease in the resultant positive unidirectional voltage impressed on control members I6, causing thereby a virtual retardation in phase of the control member voltages. Because of this retardation in phase of the voltages impressed on control members I6, the speed of machine I will be decreased,

thereby restoring the'speed of machine I to the predetermined range of operation.

Capacitance 3I and resistance 32 serve as a damping means to'prevent the speed of the machine I from overshooting the predetermined range of speed values to be maintained. The damping effect of the capacitance 3| and resistance 32 for large or substantial changes in speed of machine I is due to the fact that the charge on the capacitance 3| cannot change instantaneously relative to variations in potentials across its terminals. The capacitance 33, which is connected in shunt relation with resistance 32, permits small variations in voltage to be transmitted to control members I of electric valves I and 8 and to control these electric valves within narrowly defined ranges of operation. Capacitance 3I and resistance 32, acting in conjunction with capacitance 33, serve to control the conductivities of electric valves 1 and 3 to effect stable operation when the speed of machine I is held within narrowly defined limits; capacitance 3| and resistance 32 prevent over-shooting of the limit to be maintained, and capacitance 33 accomplishes the small or fine regulation.

Fig. 2 of the accompanying drawings diagrammatically illustrates another embodiment of my invention for controlling a dynamo-electric machine of the direct current type. The arrangement of Fig. 2 is similar in many respects to that of Fig. 1 and corresponding elements have been assigned like reference numerals. Armature 2 of machine I may beenergized from any suitable source of direct current 34, and field winding 3 of machine I may be connected to the armature circuit of machine I through a current controlling device such as an adjustable resistance 35. Electric valves I and 3 may be energized from the'alternating' current circuit 5 through a transformer 33 having a primary winding 31 and a secondary winding 33. The transformer 35 may also be provided with a secondary winding 33 for energizing cathode heating elements for electric valves I- and 3.

A source of alternating current of predetermined phase displacement for energizing control members II of electric valves I and I may be obtained by utilizing a secondary winding 43 of transformer 33 which energizes any suitable phase shifting circuit 4|. The phase shifting circuit 4I may be of the static type, and may include a capacitance 42 energizes a transformer 44 having a primary winding 45 and a secondary winding 45 provided with an electrical intermediate connection 41. Terminals of the secondary winding 43 are connected to control members I5 of electric valves 1 and 3 through current limiting resistances 23. Capacitances 43 and 43 may be connected across control members It and cathodes I5 of electric valves 1 and 3 to absorb extraneous transient voltages which may exist in the control circuits. 7

As an agency for impressing on control members I5 of electric valves 1 and 3 a potential which varies in accordance with a predetermined influence derived from machine I, I provide a suitable impedance element such as a resistance 50 which is connected between cathodes I5 of valves 1 and 3 and the electrical intermediate connection 41 of transformer winding 46. To transmit variable unidirectional currents through resistance 53 in accordance with the controlling influence, such as the speed of machine I, I provide an electronic discharge device 5|, which and a resistance 43, which .reference potential which acts in opposition to the voltage provided by armature 25 of pilot generator 24 so that the resultant voltage impressed on grid 54 varies as a difference voltage. While I have chosen to show the source of reference potential as comprising a voltage divider and a direct current source, it is to be understood that I may employ any other suitable arrangement known in the art. As a source of energization for electric discharge device 5I, I employ a transformer 53 having a primary winding 59 and secondary windings 50 and SI. Secop'da y winding 5| is connected to cathode 53 of discharge device 5I to effect energization thereof, and secondary winding 60 is connected to a rectifler 62 and an electrical wave filter 53 to impress a unidirectional voltage across anode 52 and cathode 53. The rectifier 52 may be of the full wave type and may employ elements of the dry surface contact type such as that disclosed and claimed in United States Letters Patent No. 1,640,335, granted August 23, 1927, .upon an application of Lars O. Grondahl. The electrical wave filter 63 may comprise an inductance 64, a capacitance i5 and a resistance 66. Cathode 53 of electronic discharge device 5| is connected to the lower terminal of resistance 50 through a conductor 31, and the upper terminal of resistance 53 is connected to the negative terminal of the wave filter 43 through a conductor 63.

As an agency for controlling the rate of change of the voltage impressed on grid 54 of electronic discharge device I in accordance with the volt-. age appearing across the terminals of resistance 55. I provide a damping circuit including a serially connected capacitance 63 and a resistance 13 which are connected to the grid circuit for device 5|. This damping circuit is connected to prevent hunting of the control system and affordsan arrangement for obtaining precise control of machine I during variable load conditions.

The operation of the embodiment of my invention shown in Fig. 2 will be explained by considering the machine I when it is operating as a direct current motor. Armature 2 of machine I is energized from circuit 34, and field winding 3 of machine I is energized primarily through electric valves I and 3 which control the speed of machine I. As will be well understood by those skilled in the art, the average current conducted by electric valves I and 8 may be controlled by controlling the phase of the resultant voltage impressed on control members I5. When there is substantial phase coincidence between the voltages impressed on control members I5 and the voltages impressed on the associated anodes, the average current conducted by these electric valves is maximum, and when the control voltages are displaced in the lagging direction by substantially electrical degrees relative to the respective anode voltages the average cur rent of these electric valves is substantially zero when the electric valves are energizing an inductive circuit. Phase shifting circuit 4i impresses on control members I5 of electric valves 1 and 8, through transformer 44, control voltages lag- 81118 by 90 electrical degrees the respective anode "ode 53 relative to the potential of grid 54.

voltages. The system is arranged so that the positive unidirectional control potential impressed.

on control members l6 by resistance 50 is of sufficient value to cause electric valves and 8 to transmit the requisite amount of current to maintain the speed of machine at the desired value. Electronic discharge device 5| controls the amount. of unidirectional current transmitted to resistance 50, thereby controlling the magnitude of the unidirectional control voltage appearing across its terminals and controlling the conductivities of electric valves 1 and 8 in accordance with the speed of machine Resistance 51 is adjusted so that the resultant voltage impressed on grid 54 of electronic discharge device 5| attains that value which will maintain the speed of machine at the predetermined value under steady load conditions.

If it be assumed that the speed of machine increases to a value above the predetermined value or range to be maintained, the potential impressed on grid 56 of discharge device 5| will become more positive relative to the potential of the cathode 53 to cause the device 5| to supply a larger amount of current to resistance 50, thereby increasing the positive unidirectional potential impressed on control members I6 of electric valves 1 and 8. This increase in positive potential will effect a virtual advancement in phase of the resultant voltages impressed on control members l6, causing the electric valves I and 8 to conduct a'greater value of average current and thereby increasing the energization of the field winding 3 of machine This increase in energization of field winding 3 will effect a re- Under the above assumed conditions, as the conductivity of the discharge device 5| is increased, due to the more positive voltage being impressed on grid 54, the incident increase in voltage appearing across the terminals of resistance 50 is reflected by the flow of current through resistance l0 and capacitance 69, temporarily raising in a positive direction the potential of the cath- This rise-in potential is, of course, occasioned by the charging current of capacitance 59 and introduces a compensatory effect which tends to prevent hunting of the system and permits the control arrangement to maintain the speed of machine within narrowly defined limits. While I have explained the operation of the arrangement shown in Fig. 2 for increases in speed of machine above a certain value, it is to be understood, of course, that the arrangement functions in a similar manner for decreases in speed of the machine I, tending to restore the speed of the machine to the desired value.

Fig. 3'represents another embodiment of my age variations occasioned by variations in speedof the machine The bridge circuit may cpmprise impedance elements such as resistances 12 having linear impedance-current characteristics and may also include impedance elements such as resistances 13 having nonlinear impedance-current characteristics.- Resistances I3 may be made of the material disclosed and claimed in United States Letters Patent No. 1,822,742, granted September 8, 1931, upon an application of Karl B. McEachron and assigned to the assignee of the present application.

The operation of the arrangement shown in Fig. 3 is substantially the same as that explained in connection 'with the embodiment shown in Fig. 2. The bridge circuit 1| accentuates the voltage variations of armature 25 of pilot generator 24 and provides a suitable arrangement for controlling the conductivity of electronic discharge device 5| which in turn controls the unidirectional voltage impressed on control members '56 of electric valves 1 and 8.

In Fig. 4 there is diagrammatically represented a' still further embodiment of my invention showing several elements included in the arrangement of Fig. 2, and these elements have been assigned corresponding reference numerals. The damping circuit including capacitance 59 and resistance 10 are connected to be energized inaccordance with an electrical condition, such as the current, of the armature .circuit 2 of machine A suitable impedance element such as a resistance l4 may be connected in series relation with the armature 2 of machine to produce a voltage which varies in accordance with the armature current. This voltage is introduced into the circuit for grid 54 of discharge device 5| and acts to prevent huntmg. I

The operation of the embodiment of my invention shown in Fig. 4 is substantially the same as that explained above in connection with Fig. 2. During transient conditions the voltage appearing across the terminals of resistance'f causes a charging current to flow through a circult. including capacitance 69 and resistance 10, establishing across the terminals of resistance 10 a voltage to modify the potential difference between grid 54 and cathode 53 thereby preventing hunting of machine I.

Fig. 5 shows another embodiment of my invention in which an alternating current pilot generator I5 is employed to generate an alternating voltage, the frequency of which varies in accordance with the speed of the machine I. The pilot generator 15 is provided with a field winding 16 and an armature circuit 11. In order to provide a suitable arrangement for producing an alternating voltage of peaked wave form, I provide a saturable transformer 18 having a secondary winding 19. A rectifier is connected across the terminals of secondary winding 19 to produce a unidirectional voltage the magnitude of which varies with the speed of the machine I. The output, terminals ill of rectifier 80 may be connected to cathode 53 and grid 54 of electronic discharge device 5| shown in Fig. 2.

The arrangement of Fig. 5 also operates, to control the speed of machine I under varying load conditions. The undirectional voltage appearing-across the terminals Bl of rectifier 80' varies in magnitude in accordance with the frequency of the voltage impressed on transformer 18; therefore, the conductivity of the electronic discharge device 5|, shown in Fig. 5, is controlled in accordance with the speed of machine I to effect the desired regulating action.

In Fig. 6 there is shown a modification of the embodiment of my invention shown in Fig. 5 as applied to an arrangement for controlling the 7 2,207,404 energy input to a prime mover 82 which drives a generator, such as an alternating current generator 83 having a field winding 84 and an armature circuit 85. The put to prime mover 82 may be controlled by a suitable valve controlling motor 86 having an armature member 81 and a field winding 88. Output terminals 8| of rectifier 80 may be connected to cathode 53 and grid 54 of an electronic discharge device shown in Fig. 2, and the armature and the field winding 88 of the valve motor 86 may be energized from an arrangement similar to that shown in Fig. 2.

In operation the arrangement shown in Fig. 6 performs substantially the same asthat explained in connection with Figs. 2 and 5. The frequency of the alternating voltage generated by pilot generator I5 varies in accordance with the speed of the generator 83, and the energization of the valve motor 86 is controlled to maintain the speed and the frequency of the generator 83 at a predetermined value or range of values.

Various aspects of the control system shown in Figs. 5 and 6, including the means for pro? ducing a voltage of peaked wave form, are disclosed and claimed in my copending divisional application Serial No. 219,382, filed July 15, 1938.

In Fig. 7 of the accompanying drawings there is shown another embodiment of my inventionas applied to a control system for operating a reversible direct current motor. A direct current motor 89 having field winding 90 and armature members 9| and 92 is arranged for operation in either direction of rotation. The field winding 90 may be energized from any suitable source of direct current 93 through a current controlling resistance 94. To selectively energize armature members III and 92, I provide a pair of electric valve translating apparatus 95 and 96 which are associated with armature members 8| and 92,

respectively. The electric valve translating apparatus 95 and 96 are arranged to transmit unidirectional currentto armature members 9| and 92 and the armature members 9| and 92 are arranged to rotate motor 89 in'opposite directions. The translating apparatus 95 and 96 may be energized from any suitable source of alternating current 91 and include electric valves 98, 99 and I00, IOI, respectively. These electric valves are preferably of the type employing an ionizable medium and each includes an anode I02, a cathode I03 and a control member I04.

To impress on the control members I04 alternating voltages of predetermined phase displacement relative to the respective anode voltages, I employ a phase shifting circuit I05 which may be any of the forms known in the art. The phase shifting circuit I05 comprises a capacitance I05 and a resistance I01 and impresses altion of rotation of motor 89, I provide resistances I I4 and I I5 which are associated with electric valves 98, 99 and I00, IOI, respectively. The

ternating voltages on control members I04 which so have a lagging phase displacement of substantially 90 electrical degrees relative to the respective anode voltages. A transformer I08 having a primary winding I09 and secondary windings H0 and III is connected between the phase shifting circuit I05 and control members I04 of electric valves 98 --IOI. Secondary windings H0 and III are provided with electrical intermediate connections I I2. A transformer II 3 is connected to circuit 91 to supply current to heating elements of cathodes I03 of electric valves 98'- IOI.

As an agency for controlling selectively the conductivities of electric valves 98, 99 and I00, IN to efiect control of the speed and the direcresistances H4 and H5 have a common juncture H5 and the terminals of the resistances are connected to the electrically intermediate connections II2 of secondary windings H0 and III of transformer I08. To control the current transmitted through resistances H4 and H5 in accordance with the speed and the direction of rotation of motor 89, I provide a pair of electronic discharge devices III and H8 which are preferably of the high vacuum type and each comprises an anode H9, a cathode I20 and a grid I2i. The electronic discharge devices III and H8 transmit variable unidirectional currents through resistances H4 and H5 to impress variable unidirectional control potentials on control members I04 of electric valves 98-IOI, inclusive.

To supply unidirectional current to electronic discharge devices III and H8, and to supply a positive unidirectional biasing potential for control members I04 of electric valves 98-IOI, I employ circuits I22 and I23 respectively, each of which comprises a rectifier I24 and an electrical wave filter I25 including an inductance I26, a capacitancel21 and a resistance I28. The rectifiers I24 may be of the full wave type and may include elements of the dry surface contact type. A transformer I29 may be connected between circuits I22 and I23 and a suitable source of alternating current such as circuit 91. Transformer I29 is provided with secondary windings I30, I3I and I32. The secondary winding I32 is provided with an electrical intermediate connection I33. Secondary windings I30 and I3I energize rectifiers I24 of circuits I22 and I23, respectively. Secondary winding I32 energizes the heating elements for cathodes I20 of electronic discharge devices II! and H8.

A pilot generator I34, having an armature member I35 and a field winding I30, is provided as an agency for producing a voltage which varies as the speed and the direction of rotation of motor 89 and may be mechanically coupled thereto. The pilot generator I34 may be of the direct current type. A bridge circuit I31 is connected to the armature terminals of the pilot generator I34 and may comprise linear resistances I38 and nonlinear resistances I39. The nonlinear resistances may be of the type described and claimed in the above mentioned patent of Karl E. McEachron.

A pair of damping circuits are connected between the field circuit of motor 89 and the grid circuits for electronic discharge devices III and 8 One of these damping circuits is associated with electronic discharge device III and comprises a capacitance I40 and a resistance MI, and the other is associated with discharge device H8 and comprises a capacitance I42 and a resistance I43. Resistances HI. and I43 are connectedto the bridge circuit I31 and a common juncture I44 of these resistances is connected to the cathodes I20 of discharge devices II! and H8 through a conductor I45 and through secondary winding I32 of transformer I29.

The operation of the embodiment of my invention shown in Fig. 7 will be explained by considering the arrangement when the machine 89 is operating as a direct current motor and when the system is arranged to effect control of the speed of machine 89 for either direction of rotation. If it be assumed that the. armature member of motor 89 rotates in a clockwise directhe control of the motor 89' is effected predominately by electric valves 98 and 99 which in turn are controlled by the electronic discharge device III. For this direction of rotation, the pilot generator will produce a unidirectional voltage of a predetermined polarity such that the voltage impressed on grid I2I of discharge device II! is positive. Discharge device III will conduct variable unidirectional currents through resistance H4, in accordance with speed variations of motor 89, to impress variable positive unidirectional potentials on control members I04 of electric valves 98 and 99. Circuit I22 impresses unidirectional voltages across the anodes and cathodes of electronic discharge-devices H1 and H8 through resistances II4 and H5, and circuit I23 impresses positive unidirectional potentials on control members I04 of electric valves 98-IOI. Electronic discharge devices conduct variable amounts of unidirectional current through resistances H4 and H and thereby control the magnitude of the voltages appearing across the terminals thereof. The direction of these voltages is opposite to thatprod iced by the rectifier I24 in circuit I23. Therefore, the

grids l2l by pilot generator I34, thereb pre venting hunting of'the motor 89.

While I have shown and described my inven-. tion as applied to particular systems of connections and as embodying various devices diagrammatically shown, it will be obvious to those skilled in the art that changes and modifications may be made without departing from my invention, and I, therefore, aim in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In combination, a direct current motor having an excitation circuit and a pair of armature circuits, electric translating apparatus and each comprising electric valve means associated with a difierent 'one of said armature circuits, said electric valve means each having resultant potentials impressed on control members I04 of electric valves 98--IOI is the algebraic sum of the lagging quadrature component due circuit I05, the voltage produced by rectifier I24 of circuit I23 and the voltages appearing across the terminals of resistances H4 and H5.

If it be assumed that the speed of the motor 89 increases to a value above the value to be maintained, the output voltage of the pilot generator I34 will increase correspondingly and the voltage impressed on grid I2I of discharge device III will increase in a positive direction, effecting an increase in the unidirectional current transmitted through resistance II4. This increase in current occasions a decrease in the resultant positive unidirectional voltage impressed on control members I04 of electric valves 98 and 99 and ultimately effects a decrease in the voltage impressed on armature 9|. By virtue of this decrease in armature voltage, the speed of the motor 89 will be restored to the desired value. On the other hand, if the speed decreases the system will respond in a similar manner to effect an increase in the voltage impressed on armature winding 9I, tending to restore the motor speed to the desired value.

For counterclockwise rotation, the armature winding 92 predominates and the current for this winding is supplied by electric valves I00 cause currents to flow through resistances HI and I43 which are the charging currents for capacitances I40 and I42, respectively. The polarities of 'the voltages appearing across the terminals of resistances I4I and I42 under the transient conditions will tend to modify. or compensa'te for the voltage variations impressed on a control member for controlling the conductivity thereof, means for controlling the speed and direction of rotation of said motor comprising a pair of electronic discharge devices each associated with a difierent one of said electric valve means'for impressing control voltages on the control members and each comprising a grid, 9, direct current pilot generator responsive to the speed of said motor for producing an output voltage which varies in accordance with the speed of said motor, a bridge circuit connected to the output circuit of said pilot generator, and anti-hunting means connected between said bridge circuit and the grids of said electronic discharge devices for controlling the rate of change of the potential impressed on said grid.

2. In combination, a direct current motor having an excitation circuit and a pair of armature circuits, electric translating apparatus for selectively energizing said armature circuits and each comprising electric valve means connected to a difierent one of said armature circuits, said electric valve means each having a control mem- 'ber for controlling the conductivity thereof,

for producing an output voltage responsive to the speed of said motor, a bridge circuit connected to said pilot generator for accentuating the variations in output voltage thereof, and anti hunting means connected between said excitation circuit and said bridge circuit for controlling the rate of change of the potential impressed on the grids of said electronic discharge devices. 1

3. In combination, a direct current motor having an excitation circuit and having a pair of armature circuits, translating apparatus for selectively energizing said armature circuits and comprising a pair of electric valve means each associated with a difierent one of said armature circuits, said electric valve means each being provided with a control member for controlling the conductivity thereof, a pair of electronic discharge devices each associated with a difierent one of said electric valve means for impressing av control voltage on the associated control member and each comprising a grid for controlling the conductivities thereof, means for impressing on the grids voltages which vary in accordance with the speed of said motor, and means connected between said excitation circuit and said last mentioned means for controlling the rate of ch'ange of the potential of the grids.

4. In combination, a direct current motor having a field circuit and an armature member having a pair of circuits, electric translating apparatus for selectively energizing the armature circuits to eifect rotation of said armature member in either direction and comprising a pair of electric valve means each associated with a different one or said armature circuits, each 01 said electric valve means being provided with a control member for controlling the conductivity thereof, a pair of electronic discharge devices or impressing on the control members of the electric valve means control potentials which vary in accordance with the speed of said motor, each of said devices being provided with a grid for controlling the conductivity thereof, a pilot generator for producing a voltage which varies in accordance with the speed of said motor and in accordance with the direction of rotation of said motor to eflect ductivities oi the electronic discharge devices, and means connected between the excitation circuit and the grids to control the rate of change of the potentials of the grids.

GEORGE W. GARMAM.

selective control of the con-' 

